The beta-type zeolite is a useful substance as a solid acid catalyst or an adsorbent, and, currently, a large amount of the beta-type zeolite is globally used as a catalyst in the petrochemical industry or a hydrocarbon trap for purifying the exhaust gas of an internal-combustion engine. A variety of synthesizing methods of a beta-type zeolite have been proposed. An ordinary method is a method in which a compound including tetraethylammonium ions is used as a structure directing agent (hereinafter abbreviated to “organic SDA”). Such a method is described in, for example, Patent Citation 1 below. However, although the compound including tetraethylammonium ions is expensive, most of the excessive portion is decomposed after completion of the crystallization of a beta-type zeolite, and decomposition is the only method that can remove the portion incorporated into crystals, and therefore it is not possible to collect and recycle the compound. Therefore, a beta-type zeolite manufactured using the above method is expensive. Furthermore, since tetraethylammonium ions are incorporated into crystals, it is necessary to remove tetraethylammonium ions through firing when a beta-type zeolite is used as an adsorbent or a catalyst. The exhaust gas at this time causes environmental contamination, and a large amount of a chemical is required for a detoxifying treatment of a synthesis mother liquid. As such, since the synthesizing method of a beta-type zeolite using tetraethylammonium ions is a manufacturing method which is not only expensive, but also causes a large environmental load, there has been a demand for realization of a manufacturing method in which the organic SDA is not used.
Under the above circumstance, in recent years, a synthesizing method of a beta-type zeolite in which the organic SDA is not used has been proposed in Patent Citation 2. In the document, a silica source, an alumina source, an alkali source and water are mixed so as to form a reaction mixture having a specific composition; a beta-type zeolite not including an organic compound which has a SiO2/Al2O3 ratio of 8 to 30 and an average particle diameter of 150 nm or more is used as a seed crystal, the beta-type zeolite is added to the reaction mixture at a proportion of 0.1 mass % to 20 mass % with respect to the silica component in the reaction mixture; and the reaction mixture to which the seed crystal is added is enclosure-heated at 100° C. to 200° C., thereby synthesizing a beta-type zeolite without using the organic SDA.
However, in a case in which the beta-type zeolite is used as a catalyst in the petrochemical industry or a hydrocarbon trap for purifying the exhaust gas of an internal-combustion engine, it is advantageous to increase the Si/Al ratio from the viewpoint of performance improvement. A method for increasing the Si/Al ratio in the beta-type zeolite is described in, for example, Patent Citation 3, and a method in which a water vapor treatment and an acid treatment are carried out sequentially is known.
[Patent Citation 1] U.S. Pat. No. 3,308,069
[Patent Citation 2] Pamphlet of the International Publication No. 2011/013560
[Patent Citation 3] Japanese Patent Application Laid-Open No. 2010-215434